JPH08134224A - Redispersible resin - Google Patents

Abstract

PURPOSE: To obtain a redispersible resin having satisfactory antiblocking properties by mixing a particulate water-dispersible resin having a specific glass transition temp. with a particulate water-soluble resin having a given glass transition temp. and a given acid value. CONSTITUTION: Methyl methacrylate, ethyl acrylate, methacrylic acid, etc., are dropped with stirring into water containing an emulsifying agent and a polymerization initiator, and are polymerized with stirring at about 70-80 deg.C. The resulting resin emulsion is spray-dried to obtain a particulate water- dispersible resin (A) having a glass transition temp. of 15 deg.C or higher. Methyl methacrylate, butyl acrylate, methacrylic acid, and a polymerization initiator are dropped into an aqueous PVA solution, and are polymerized with stirring at about 80-90 deg.C. The resin yielded is dissolved in an aqueous alkali solution, and the resin solution is spray-dried to obtain a particulate water-soluble resin (B) having a glass transition temp. of 15 deg.C or higher and an acid value of 30 mgKOH/g or higher. The resins (A) and (B) are mixed in a weight ratio of (80-20)/(20-80) to obtain the objective resin having a lowest film-forming temp. of 20 deg.C or lower.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a redispersible resin, and more specifically, it has good blocking resistance during powder spray drying and is redispersible when redispersed in water. And a redispersible resin having good film-forming property of the redispersion liquid.

[0002]

2. Description of the Related Art In recent years, as a measure for protecting the global environment, synthetic resins used as coating materials and various additives are
From the viewpoints of pollution-free, resource saving, workability, etc., solvent-based materials are being shifted to dispersion-type or emulsion-type water-based materials such as water-dispersible resins and water-soluble resins. Of these dispersion-type water-based materials, a powdered resin that is easily redispersed in water by mixing with water and stirring is said to be a water-redispersion type resin.
This is because water is added immediately before use, compared to conventional emulsion-type water-based materials, easier to wrap, easier to transport, has good storage stability, and is free from fear of freezing.
It has features such as easy disposal of the packaging container after use.

Usually, as a method for obtaining a redispersion type resin, a spray drying method, a freeze drying method, a reduced pressure drying method and the like can be mentioned. Generally, from the viewpoint of productivity and the like, the emulsion resin is sprayed and dispersed in hot air to obtain the hot air. A spray-drying method is widely adopted in which powder is rapidly dried while being transported by.

However, when a redispersible resin powder is produced by such a spray drying method, if an emulsion resin having a low minimum film forming temperature is used, the inner wall of the spray drying tower and an atomizer for spraying the emulsion resin are used. Adhesion and deposition on the mouth, powder outlet, and in a carrier pipe that carries the spray-dispersed powder with hot air (hereinafter referred to as the inner wall of the spray dryer), and the fusion of the powder particles occurs. There is a problem that blocking is intense and it becomes a lump and does not redisperse even if water is added, and it is possible to efficiently produce a redispersion type resin powder having a low minimum film forming temperature of 20 ° C. or lower required for coating materials and the like. There wasn't.

[0005]

Therefore, in order to solve the problem of the redispersion type resin powder by the spray drying method, the water dispersion type inorganic particles are atomized simultaneously with the emulsion resin in the spray drying tower, A method of preventing re-dispersion type resin powder in the form of particles in an air stream from being covered with the inorganic particles so as to prevent adhesion to the inner wall of the spray dryer, deposition and fusion of the powders (Japanese Patent Publication No. 55-50971). ) Is proposed.
However, in the redispersion type resin powder obtained by such a method, since the inorganic particles remain on the surface of the resin powder, the transparency of the coating film as a coating material is lowered, or the resin particles are essentially fused easily. Since the resin is present inside the redispersion type resin powder, there is a problem in that the powder particles are blocked during storage such as loading, resulting in poor long-term storability.

[0006] Further, a method has been proposed in which a large amount of polyvinyl alcohol is added as a protective colloid to an emulsion resin having a low minimum film forming temperature, and spray drying is performed (Japanese Patent Publication No. 46-12907). A redispersion liquid using a resin having a low compatibility with alcohol causes phase separation, and when this is used as a coating material, the film formation becomes defective and a uniform coating film cannot be obtained. Therefore, by using a large amount of polyvinyl alcohol, it is possible to prevent fusion of the resin powders to each other and improve the dispersibility of the resin in the emulsion, but since a large amount of polyvinyl alcohol is used, coating There is a problem that the original physical properties of the emulsion are difficult to be expressed, such as poor water resistance and weather resistance of the film.

Further, JP-A-5-194681 discloses a polymer powder having a core-shell particle structure having an alkali-soluble emulsion polymer shell and a water-insoluble emulsion polymer core. Manufacturing methods have been proposed. However, even with a polymer powder having such a specific particle structure, it is not possible to obtain a redispersible resin that simultaneously satisfies both the blocking resistance of the polymer powder and the low minimum film forming temperature of 20 ° C. or lower. Have difficulty.

[0008]

Means for Solving the Problems As a result of intensive studies on the above problems, the present inventors have found that a water-dispersible resin powder made of a resin having a glass transition temperature (hereinafter referred to as Tg) of 15 ° C. or higher. And a water-soluble resin powder having a Tg of 15 ° C. or more and a specific acid value or more are separately or simultaneously mixed and spray-dried, and when this is hydrolyzed under alkaline conditions to form a redispersion liquid, the resin powder It was found that a redispersible resin capable of reducing the blocking resistance of the body and the minimum film-forming temperature of the redispersion liquid was obtained, and completed the present invention.

That is, the redispersible resin of the present invention has a water-dispersible resin powder (A) having a Tg of 15 ° C. or higher obtained by spray drying and a Tg of 15 ° C. obtained by spray drying.
The water-soluble resin powder (B) having an acid value of 30 mgKOH / g or more is contained.

The present invention will be described in detail below. To obtain the redispersible resin of the present invention, the water-dispersible resin powder (A) and the water-soluble resin powder (B) are separately spray-dried, and then each powder is mixed. How to obtain, or
There is a method in which an emulsion resin for obtaining the water-dispersible resin powder (A) and an emulsion resin for obtaining the water-soluble resin powder (B) are mixed and simultaneously spray-dried. However, in the latter method of simultaneously spray-drying to obtain a redispersible resin, when an emulsion resin for obtaining a water-soluble resin powder (B) having a low acid value is used, the resin is sprayed into a spray-drying apparatus at the time of spray-drying. It is preferable to use an emulsion resin having a high acid value because adhesion of the resin and blocking of the resin powders easily occur.

Both the water-dispersible resin powder (A) and the water-soluble resin powder (B) used in the present invention must have Tg of 15 ° C. or higher, preferably 25 ° C. or higher. This is because if the Tg is less than 15 ° C., during spray drying of the emulsion resin, resin powder is likely to adhere to or deposit on the inner wall of the spray dryer, or the resin powder is blocked from each other. This is because the redispersibility is remarkably reduced due to the formation of the product.

That is, the water content is 3% by the spray drying method.
In order to obtain a powder having the following normal dryness, it is necessary to set the temperature of the powder outlet to 45 ° C. or higher. However, due to the physical properties of the emulsion resin used, the temperature of the powder outlet should be the same as that of the emulsion resin. When the temperature is higher than Tg by 30 ° C. or more, blocking between the resin powder particles occurs, and when the temperature is higher than Tg of the emulsion resin by 40 ° C. or higher, resin lumps are formed. That is, since the minimum film forming temperature of the redispersion liquid is in the vicinity of the Tg of the emulsion resin, as a result, there is no sticking in the spray drying device or blocking between the resins, and the powder is spray-dried and powdered. In order to obtain a body, it is necessary to pulverize an emulsion resin having a Tg of 15 ° C. or higher, and the Tg of the resulting resin has a lower limit of 15 ° C.

In the present invention, the water-dispersible resin powder (A)
Is not particularly limited as long as it is redispersible in water and has a Tg of 15 ° C., and specific examples include acrylic resins, vinyl chloride resins, vinyl acetate resins, styrene / acrylic resins, polyvinyl alcohol resins. (Hereafter, E
VA resin), olefin resin, and copolymers of the above resins, modified resins and the like. The water-dispersible resin powder (A) is produced by spray drying the emulsion resin (a), and the method for producing the emulsion resin (a) is not particularly limited as long as redispersibility and dispersion stability are secured. However, the emulsion polymerization method is preferable as a method for producing the emulsion resin (a) having good dispersion stability and a small primary particle diameter.

The water-soluble resin powder (B) used in the present invention is re-dispersed in water under alkaline conditions and then dissolved to lower the minimum film forming temperature of the water-dispersible resin powder (A). And Tg of 15 ° C or higher, acid value of 30 mgK
It is important that it is OH / g or more, and preferably,
It is a resin powder having a Tg of 25 ° C. or higher and an acid value of 40 mgKOH / g or higher. Although this water-soluble resin powder (B) has different water solubility depending on the molecular weight, its acid value must be at least 30 mgKOH / g in order to exert the effect of lowering the minimum film-forming temperature. Is. This is because when the acid value is less than 30 mgKOH / g, the solubility in water is poor and the effect of lowering the minimum film forming temperature of the redispersion liquid is small. Specifically, when the molecular weight of the emulsion resin (b) used is small, the acid value is 30 mgKOH.
/ G or more, 40 mgKOH / g when the molecular weight is large
As described above, good water solubility is obtained, and the effect of lowering the minimum film forming temperature of the redispersion liquid using the same can be exhibited.

The water-soluble resin powder (B) is soluble in water and has a Tg of 15 ° C. or higher and an acid value of 30 mgKO.
It is not particularly limited as long as it is H / g or more, and specific examples thereof include a polycarboxylic acid resin obtained by copolymerizing an acid monomer having a double bond such as acrylic acid and methacrylic acid. In order to improve the compatibility with the water-dispersible resin powder (A), vinyl chloride resin, vinyl acetate resin, styrene / acrylic resin, EVA resin, olefin resin, etc. are copolymerized with the polycarboxylic acid resin. It is also possible. The method for producing the water-soluble resin powder (B) is not particularly limited, but the emulsion resin (b) obtained by the suspension polymerization method or the emulsion polymerization method is pulverized by spray drying. Obtainable.

The mixing ratio of the water-dispersible resin powder (A) and the water-soluble resin powder (B) can be arbitrarily selected depending on the required minimum film-forming temperature of the redispersible resin. ,
From the viewpoint of redispersibility and minimum film forming temperature, the content of the water-soluble resin powder (B) is preferably 20 to 80% by weight, more preferably 30 to 70% by weight. This is because the redispersion liquid containing too much water-soluble resin powder (B) cannot take the form of the water-dispersible resin and becomes the form of the water-soluble resin, so that the viscosity tends to remarkably increase. On the contrary, if the amount is too small, the effect of lowering the minimum film forming temperature tends to be insufficient.

The mechanism by which the water-soluble resin powder (B) lowers the minimum film forming temperature under alkaline conditions is not certain at this point, but the water-soluble resin powder (B) is water-soluble. The water-dispersed resin powder (A) is plasticized by adsorbing or diffusing on the surface of the dispersion-type resin powder (A), and the deformation resistance of each powder decreases.
It is considered that this is because the fusion property between the powder (A) and the powder (B) is improved.

The spray drying method for obtaining the water-dispersible resin powder (A) and the water-soluble resin powder (B) of the present invention is not particularly limited, and a commonly used spray dryer is used. Can be done by To obtain the redispersible resin of the present invention, the water-dispersible resin powder (A) and the water-soluble resin powder (B) are separately spray-dried, and then each powder is mixed. There is a method of obtaining it, or a method of mixing the emulsion resin for obtaining the water-dispersible resin powder (A) and the emulsion resin for obtaining the water-soluble resin powder (B) and simultaneously spray-drying. However, in the latter method of simultaneously spray-drying to obtain a redispersible resin, when an emulsion resin having an acid value of less than 40 is used to obtain the water-soluble resin powder (B), spraying is performed during spray drying. It is preferable to use an emulsion resin having a high acid value because adhesion to the inside of a drying device and blocking between resins are likely to occur. As the drying temperature condition, it is preferable to increase the temperature difference between the emulsion spray port and the powder outlet of the spray drying tower because the drying efficiency of the emulsion resin will be good. As the dispersion medium used for redispersing the redispersible resin of the present invention, water or an alkaline solvent may be arbitrarily selected so that the redispersion liquid is under alkaline conditions.

[0019]

EXAMPLES The present invention will be described below with reference to examples.
However, "part" in the examples means "part by weight".

The evaluation methods in the examples are as follows. -Acid value: mg number of KOH necessary to neutralize 1 g of resin (mgKOH / g) -Spray state: The spray state at the atomizer outlet in the spray dryer was visually observed. ○: There is no fused substance and the atomization is uniform. × ... Fused substance is accumulated and the atomization is non-uniform. ・ Blocking: The state of the powder dried by spraying is observed with an electron microscope (manufactured by JEOL Ltd .; trade name: JSM-5200)
Observed at. ◯: Free-flowing powder with no lump of 1 mm or more. X: A powder having no fluidity and having a lump of 1 mm or more. Redispersibility: 100 parts of resin powder was added to 150 parts of pure water, and the dispersion state after stirring at 150 rpm for 1 minute was visually observed. ○: Dispersed in milky white, and no aggregation or precipitate was observed. X: Melts and / or thickens.

[Example 1] <Production of water-dispersible resin powder (A1)> In a 2-liter four-necked flask, 600 parts of water and polyoxyethylene nonylphenyl ether (manufactured by Kao Corporation; trade name Emulgen) 910) 8.0 parts and 0.6 parts of potassium persulfate were added,
After replacing with nitrogen gas, the temperature was raised to 70 ° C. while stirring at 150 rpm in a nitrogen gas stream. Next, a mixture of 260 parts of methyl methacrylate, 132 parts of ethyl acrylate, 8 parts of methacrylic acid, and 5.0 parts of sodium dialkylsulfosuccinate (manufactured by Kao Corporation; trade name Perex OTP) was placed in the flask for 3 hours. Dropped. Then 7
After holding at 0 ° C. for 2 hours, the temperature was raised to 80 ° C. and held for another 2 hours to terminate the polymerization, and milky white emulsion resin (a1) (solid content 40.5%, weight average molecular weight 300,000).
I got

The emulsion resin (a1) was dried using a spray dryer (Okawara Koki Co., Ltd .; trade name L-8 type) at a chamber inlet temperature of 120 ° C., a chamber outlet temperature of 70 ° C. and an atomizer rotation speed of 25,000 rpm. And spray-dried to obtain a water-dispersible resin powder (A1). At this time, the sprayed state was good, and no adhesion of the emulsion resin and / or powder was observed on the inner wall of the chamber and the inside of the transfer pipe. The obtained powder (A1) has Tg
(Calculated value) 46 ° C, minimum film forming temperature 43 ° C, average particle size 3
It was 0 μm, the water content was 2.2%, and blocking between the powders (A1) was not observed at all. Further, when the powder (A1) was observed with an electron microscope, it was found that primary particles having an average particle diameter of 1 μm or less were secondary-aggregated to form particles having an average particle diameter of about 30 μm. .

<Production of Water-Soluble Resin Powder (B1)> In a 2-liter four-necked flask, 800 parts of water and 1.0 part of polyvinyl alcohol (saponification degree 88%, polymerization degree 1000) 1.0
The parts were dissolved. Next, methyl methacrylate 208
Parts, 168 parts of normal butyl acrylate, 24 parts of methacrylic acid, 6.0 parts of normal dodecyl mercaptan,
A monomer solution in which 2.0 parts of azobisisobutyronitrile was dissolved was put into the flask, and after nitrogen gas replacement,
It heated at 80 degreeC for 2 hours, stirring violently under nitrogen gas stream. After that, the temperature is raised to 90 ° C., and after heating for 2 hours, further 1
It heated at 20 degreeC and distilled off the residual monomer with water, and obtained the slurry. The resulting slurry is filtered and washed,
Drying with a hot air dryer at 50 ° C., white granular powder acrylic resin (average particle size 150 μm, polymerization average molecular weight 10,000, T
g36 ° C., acid value 36 mg KOH / g) was obtained. 100 parts of this granular powder was put into 900 parts of an aqueous solution of 0.5% sodium hydroxide, heated to 60 ° C., and completely dissolved to obtain a transparent polymer solution (b1). The solution (b1) was heated at a chamber inlet temperature of 120 using a spray dryer (Okawara Koki Co., Ltd .; trade name L-8 type).
℃, outlet temperature 60 ℃, atomizer rotation speed 30000r
It was set to pm and spray-dried to obtain a water-soluble resin powder (B1) as white granular powder.

Thus, the acrylic resin is further dissolved in water and spray-dried because the primary particle diameter of the white granular powder is 150 μm, the water dissolution rate after redispersion is slow, and the dispersion stability is poor. Therefore, it is for obtaining a powder having fine primary particles. The sprayed state was good, no adhesion was observed on the inner wall of the chamber and the inside of the transfer tube, the average particle size of the obtained powder was 30 μm, the water content was 2.2%, and no blocking was observed at all.

<Production of Redispersion Liquid> A redispersible resin obtained by mixing 50 parts of the water-dispersible resin powder (A1) and 50 parts of the water-soluble resin powder (B1) is put into 150 parts of pure water. As a result, a redispersion liquid was obtained, and the redispersibility was good, and the minimum film forming temperature of this redispersion liquid was 15 ° C.

[Example 2] <Production of water-dispersible resin powder (B2)> 600 parts of water and fatty acid soda soap (Kao Corporation; trade name: Flake Marcel) 4 in a 2-liter four-necked flask. After adding 0.0 part and 1.2 parts of potassium persulfate and substituting with nitrogen gas, the temperature was raised to 70 ° C. while stirring at 150 rpm in a nitrogen gas stream. Next, 180 parts of methyl methacrylate, 140 parts of normal butyl acrylate, 80 parts of methacrylic acid,
A mixture of 6 parts of normal dodecyl mercaptan and 6.0 parts of sodium dialkylsulfosuccinate (manufactured by Kao Corporation; trade name Perex OTP) was added dropwise over 3 hours at 70 ° C.
After the temperature was maintained for 2 hours, the temperature was raised to 80 ° C. and the temperature was maintained for 2 hours to terminate the polymerization to obtain a milky white emulsion resin (b2) (solid content 40.3%, weight average molecular weight 150,000).

This emulsion resin (b2) was used in a spray dryer (Okawara Koki Co., Ltd .; trade name L-8 type).
The chamber inlet temperature was 120 ° C., the outlet temperature was 70 ° C., the atomizer rotation speed was 25,000 rpm, and spray drying was performed to obtain a water-soluble resin powder (B2). The atomized state was good, no adhesion was found on the inner wall of the chamber and the transfer pipe, and the obtained powder had a Tg (calculated value) of 43 ° C. and an acid value of 120 mg.
KOH / g, average particle diameter 26 μm, water content 2.0%, no blocking was observed.

<Production of Redispersion Liquid> A mixture of 50 parts of the water-dispersible resin powder (A1) and 50 parts of the water-soluble resin powder (B2) was mixed with 0.5% aqueous sodium hydroxide solution 150.
When the redispersion liquid was obtained by throwing it into the chamber, the redispersibility was good, and the minimum film forming temperature of this redispersion liquid was 7 ° C.

[Examples 3 and 4, Comparative Examples 1 to 3] Example 1
A water-dispersible resin powder (A
2), (A3) and water-soluble resin powders (B3) to (B)
5) was obtained. Spray dried state of each emulsion resin,
Table 1 shows the blocking properties of the obtained powders (A) and (B). However, the powders (A3) and (B4) could not be evaluated for redispersibility and the minimum film-forming temperature, because a fusion product of the emulsion resin was deposited at the atomizer port during spray drying and no powder was obtained.

[0030]

[Table 1] The symbols in the table are as follows. MMA: Methyl Methacrylate EA: Ethyl Acrylate BA: Butyl Acrylate MAA: Methacrylic Acid

These resin powders were mixed at the compounding ratio shown in Table 2 and the redispersibility and the minimum film forming temperature were measured. The results are shown in Table 2.

[0032]

[Table 2]

In each of Examples 3 and 4, the redispersibility is good, there is no blocking between the powder particles, and the performance of having the minimum film forming temperature of 20 ° C. or lower is exhibited. In Comparative Example 1, since the acid value of the water-soluble resin powder (B5) is 25 mgKOH / g, the redispersibility of the mixed redispersible resin is good, but the minimum film-forming temperature is 20 ° C. or lower. There wasn't. In Comparative Example 2, since the water-soluble resin powder (B) was not used, the minimum film forming temperature did not decrease. Comparative Example 3
Since the water-dispersible resin powder (A) was not used, the form of the redispersed resin could not be expressed and the water-soluble resin had a high viscosity.

As described in detail above, according to the method of the present invention, it is possible to obtain a redispersion liquid having a minimum film-forming temperature of 20 ° C. or less under alkaline conditions, and redispersion having good blocking resistance. Such a resin can be efficiently obtained by spray drying, and is particularly suitable as a resin for coating materials such as paints.

Claims (2)

[Claims] 1. A water-dispersible resin powder (A) having a glass transition temperature of 15 ° C. or higher obtained by spray drying, and a glass transition temperature of 15 ° C. or higher and an acid value of 30 mgKOH obtained by spray drying. / G or more of the water-soluble resin powder (B), which is a redispersible resin. 2. The redispersible resin according to claim 1, wherein the redispersion liquid dispersed in water has a minimum film forming temperature of 20 ° C. or lower under alkaline conditions.